EP2147300B1 - Method and device for non-destructive material testing of a test object using ultrasonic waves - Google Patents

Method and device for non-destructive material testing of a test object using ultrasonic waves Download PDF

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Publication number
EP2147300B1
EP2147300B1 EP08735834A EP08735834A EP2147300B1 EP 2147300 B1 EP2147300 B1 EP 2147300B1 EP 08735834 A EP08735834 A EP 08735834A EP 08735834 A EP08735834 A EP 08735834A EP 2147300 B1 EP2147300 B1 EP 2147300B1
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Prior art keywords
test object
surface
characterized
method according
test
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German (de)
French (fr)
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EP2147300B8 (en
EP2147300A1 (en
Inventor
Rainer Boehm
Matthias Goldammer
Werner Heinrich
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Siemens AG
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Bundesanstalt fuer Materialforschung und Pruefung (BAM)
Siemens AG
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Priority to PCT/EP2008/054093 priority patent/WO2008138684A1/en
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/04Analysing solids
    • G01N29/11Analysing solids by measuring attenuation of acoustic waves
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/04Analysing solids
    • G01N29/06Visualisation of the interior, e.g. acoustic microscopy
    • G01N29/0654Imaging
    • G01N29/069Defect imaging, localisation and sizing using, e.g. time of flight diffraction [TOFD], synthetic aperture focusing technique [SAFT], Amplituden-Laufzeit-Ortskurven [ALOK] technique
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/44Processing the detected response signal, e.g. electronic circuits specially adapted therefor
    • G01N29/4463Signal correction, e.g. distance amplitude correction [DAC], distance gain size [DGS], noise filtering
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00Indexing codes associated with group G01N29/00
    • G01N2291/04Wave modes and trajectories
    • G01N2291/044Internal reflections (echoes), e.g. on walls or defects
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00Indexing codes associated with group G01N29/00
    • G01N2291/10Number of transducers
    • G01N2291/101Number of transducers one transducer

Description

  • The invention relates to a method for nondestructive material testing according to the preamble of claim 1. Furthermore, the invention relates to a corresponding device according to claim 16.
  • In the case of many massive and sometimes massive products as well as intermediates, their internal structure must be investigated for material defects. This requires non-destructive testing methods that provide information about the internal, non-observable structure. This is particularly necessary for mechanically stressed components.
  • For example, steel components are forged after casting to be subsequently turned into final shape. In this case, the examination for internal material defects can already take place after forging.
  • Usually, such metal parts are tested with ultrasound. The sound waves are detected, which are reflected at interfaces in the material. With the duration of the reflected sound wave whose distance traveled can be determined. By sounding in from different directions, further information about the material defect (s) can be obtained. From this, for example, material defects can be located. For example, the geometric orientation of the material defect can be determined in this way. From the shape of the reflected sound waves conclusions can be drawn on the nature of the material defect.
  • By scanning the surface of the test object with an ultrasound detector and recording the acquired data, the volume accessible to ultrasound can be fully examined. From the collected data leaves generate an image that can be used for review.
  • There are several possibilities for determining the size of the material defects. For example, during scanning, the extent of the material error can be read directly. However, this requires that the spatial resolution is smaller than the spatial extent of the material defect. The spatial resolution is limited by the wavelength used and the size of the aperture and thus by the diffraction of the sound waves.
  • The size of the material error can also be determined by the amplitude of the reflected signal. This also allows the size of such material errors to be determined that are smaller than the spatial resolution of the method. However, the amplitude of the reflected signal also depends on other parameters, such as the orientation of the material defect or the reflection properties at the interface.
  • As the size of the material defect decreases, the amplitude of the reflected signal decreases. The distance to the interfering signals is too small to identify the material error from a single amplitude-transit time diagram. Conveniently, a distance of +6 dB between the measuring signal and the interfering signal is required.
  • The spatial resolution can be optimized by focusing the sound waves with the help of suitable probes. In this case, the focussing can be narrowed, the wider the probe is in relation to the wavelength. The focusing causes a higher sound pressure.
  • FIG. 4 shows a schematic sectional view of a test article 10 with a material defect 30. On the outside of the test object 10 is a test head 16, which is designed as a focusing probe. Of the Probe 16 are focused sound waves 32, 34 and 36 emitted. The solid line represents the wavefront of the current sound wave 32. The dashed lines represent the wavefronts of the earlier sound waves 34 and the later sound waves 36. The focused sound waves 32, 34 and 36 propagate along a predetermined direction with laterally limited extension.
  • The probe 16 moves along the scan 10 surface along a scan direction 38 during scanning. However, focus only occurs within the near field of the probe 16. The greater the width of the probe 16 perpendicular to the emission direction, the greater the distance of the detectable material defect 30 can be.
  • One possibility for evaluating the material errors is the evaluation of the amplitude according to the distance-gain-size method (AVG method). Based on the amplitude of the material error is assigned a replacement reflector size, which would produce a perpendicular sonicated free circular surface. If the detected signal is significantly larger than the noise signal or noise signal, the evaluation of the amplitude according to the AVG method is easily possible. The reflector must be located on the acoustic axis of the sound field of the test head 16. From the dependence of the amplitude of the distance to the probe 16 corresponds to the detected amplitude of a reflector size with known geometry and orientation to the acoustic axis. If, on the other hand, the detected amplitude is smaller than the noise signal or of a comparable order of magnitude, the material error can not be identified from the amplitude-transit time diagram.
  • Another way to improve spatial resolution is the "synthetic aperture-focus technique" (SAFT), which uses a small non-focusing probe. This is done with a two-dimensional mechanical scanning of Test object calculated a three-dimensional image of the test object.
  • Martin Spies and Winfried Jager describe in "Synthetic aperture focusing for defect reconstruction in anisotropic media" (Ultrasonics 41 (2003), pages 125 to 131 ) a SAFT method for anisotropic media. In such media, the group velocity of the ultrasonic signal depends on the propagation direction. As a consequence, the signal is skewed relative to the actual propagation direction. In order to take the anisotropy into account, a displacement amplitude for the wave field is determined at a position R j , which is then used to actually calculate the image using the SAFT algorithm.
  • Ahmed Yamani describes in "Three-Dimensional Imaging Using a New Synthetic Aperture Focusing Technique" (IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, vol. 44, number 4, July 1997, pages 943 to 947 ) a SAFT method using multifrequency ultrasound signals. In this method, the received signal is subjected to a fury transformation with respect to the coordinates x and y via the synthetic 2D aperture, so that the pressure field is then in the form of an angle spectrum.
  • In FIG. 5 For explanation of the SAFT process, a schematic sectional view of a test article 10 with a material defect 30 is shown. On the outside of the test object 10 is the test head 16. The test head has compared to FIG. 4 a relatively small diameter and is not focused. From the test head 16 spherical shell-shaped sound waves 42, 44 and 46 are emitted. The wavefront of the current spherical shell-shaped sound wave 42 is represented by a solid line. The dashed lines represent the wavefronts of the former spherical shell-shaped sound waves 44 and the later spherical shell-shaped sound waves 46. A comparison of FIG. 4 and FIG. 5 illustrates that the wavefronts 32, 34 and 36 of the focused sound waves on the one hand and the wavefronts 42, 44 and 46 of the spherical shell-shaped sound waves on the other hand are oppositely curved.
  • The test object 10 is divided by the SAFT method of a computer into volume elements. Each volume element is considered as a reflector during the scan. The reflected signal components from different positions of the probe 16, which belong to the same volume element, are recorded and added in phase with the assistance of the computer. In this way, echo signals of large amplitude are obtained only for those places with actual reflection due to constructive interference. For locations without actual reflection, the echo signals are canceled due to destructive interference. The scanning and arithmetic operation simulates constructive interference an ultrasonic detector whose size corresponds to the scanned area and which is focused on a location.
  • From this, the position of the material defect and, in the case of an extensive material defect, its size within the scope of the resolution can be determined. The accuracy is approximately comparable to that in the scanned area in the aforementioned method using the focused sound waves. In the SAFT method, the spatial resolution is not limited by the dimensions of the probe 16, so that a high spatial resolution is possible.
  • In the SAFT method, in each pixel in the error expectancy range, all possible reflected signal components are added with a time shift which the signal components would have if the pixel were the source of a reflected wave. The time shift, which corresponds to the phase position, results from the geometric relationships between the probe 16 and the pixel, in particular from the distance between the probe 16 and the pixel. Now, if the pixel is actually the source of a reflected wave, then the amplitude at that location increases with the number of different positions of the probe 16 from which the material error was detected. For all other pixels, the phases do not match, so that ideally the sum approaches zero, or at least is very small.
  • The SAFT method is mostly used to achieve a high spatial resolution. It is in principle a focusing method in which the resolution limit results from the wavelength and the synthetic aperture. The synthetic aperture is determined by the angular range from which the material error is detected. The aperture is limited by the movement of the probe 16 and the divergence of the sound field.
  • The test object may be, for example, a rotor of a gas or steam turbine, which is used in particular for power generation. Such a rotor is exposed during operation of a high stress. The speed of the rotor corresponds to the grid frequency of the respective power grid. For example, in a power grid with a mains frequency of 50 Hz, a speed of 3000 revolutions per minute is required. At such high speeds large centrifugal forces occur on the rotor. The centrifugal forces increase with the diameter of the rotor. The larger the turbine is designed, the stronger the centrifugal forces.
  • When starting the turbine, the rotors are particularly heavily loaded thermally in the tangential direction. In this phase, the rotor is initially cold and is brought by the hot combustion gases from outside to inside to operating temperature. Therefore, the number of starts for the life of the turbine has a special meaning. The tangential load is greatest for the rotor in the region of its central bore. Therefore, material defects near the bore have a significant impact on the longevity of the turbines. Particularly in the coming generation of turbine wheel disks, a significant increase in the detection sensitivity for axially-radially oriented material defects is required. A sufficiently accurate determination of the axial-radial oriented material defects is not possible with the previous test methods.
  • Due to the higher performance of the newer gas or steam turbines, the requirements increase that the rotor is free from material defects. The size of the rotors also increases, which results in longer ultrasonic paths during material testing. Due to the greater path length of the ultrasound, the minimum size of the detectable material defects increases in the inner region of the rotor. Thus, there is a need for a method that also enables material defect determination for large components.
  • It is an object of the invention to provide an improved method for finding and / or identifying material defects in a test article, which is also at relative large inspection items a material defect determination with sufficient accuracy allows.
  • This object is achieved by the subject matter of claim 1.
  • According to the invention, it is provided that an angle-dependent amplitude distribution is used in the sound field of the test head.
  • The core of the invention lies in a modified SAFT method in which the angle-dependent amplitude distribution in the sound field of the test head is taken into account. In this way, different sensitivities, which depend on the angle, can be considered. The amplitudes of the individual reflected signals are dependent on the amplitude distribution in the sound field of the probe. It uses the spatial sound pressure distribution of the probe to determine the amplitudes of the reflected sound waves. In the conventional SAFT method, the information about the amplitude is lost.
  • For example, from the angle-dependent amplitude distribution, a correction factor is determined which corresponds to the average sensitivity along the path through the sound field of the test head. The correction factor is determined by integration over the amplitude distribution of the test head.
  • Preferably, the amplitudes of the sound waves are added in phase within a predetermined angular interval about the acoustic axis. In this case, a test head with a small Schalbündeldivergenz, e.g. 3 ° to 5 ° at -6 dB.
  • Furthermore, ultrasonically applying the test specimen at different angles of incidence with respect to the surface element at the surface of the test object respectively. Since flaws often have a preferred direction of elongation, according to the invention the scanning of the surface of the test article and the variation of the insonification angles can be adapted to the geometry of the test article and the alignment of the material defects.
  • For example, the insonification angles lie within a cone whose axis of symmetry forms the normal of the respective surface element.
  • In a specific embodiment it can be provided that the surface or at least the surface portion of the test object is scanned along a predetermined line. Due to the different angles of incidence, the volume of the test object can be completely detected without scanning the entire surface.
  • Preferably, the surface or at least the surface portion of the test article is scanned rasterized according to a predetermined scheme. This scheme can be adapted to the geometry of the test object and / or the material defect.
  • Furthermore, the surface or at least the surface portion of the test object can be completely scanned.
  • For example, the insonification angles are between 0 ° and 50 °, preferably between 0 ° and 30 °.
  • In particular, the method can be provided for an at least partially rotationally symmetric test object. In this case, the scanning can be particularly easily adapted to the geometry of the test object. This is especially true when the method is provided for an at least partially cylindrical test object.
  • In this case, the insonification direction preferably has a radial, tangential and / or axial component with respect to the surface of the cylindrical test object. This also particularly flat formed material errors can be detected.
  • In the preferred embodiment, the method is provided for material testing a metal test article, particularly for material testing of a forged component. Particularly suitable is the method for the material testing of a turbine wheel.
  • Furthermore, the invention relates to a device for nondestructive material testing of an at least partially massive test object, which is provided for the method described above.
  • Preferably, the device comprises at least one test head for emitting ultrasonic waves and for detecting the ultrasonic waves reflected within the test object.
  • In particular, the test head is pivotable, so that the insonification direction with respect to the surface normal of the surface of the test object is variable.
  • Finally, the test head is pivotable with respect to the surface normal of the surface of the test object between 0 ° and 60 °, preferably between 0 ° and 30 °.
  • Further features, advantages and particular embodiments of the invention are the subject of the dependent claims.
  • Hereinafter, the method according to the invention in the figure description with reference to preferred embodiments and with reference to the accompanying drawings will be explained in more detail. Show it:
  • FIG. 1
    3 is a schematic sectional side view of a test object and a test head according to a preferred embodiment of the method according to the invention,
    FIG. 2
    1 is a schematic sectional view from above of the test object and the test head according to the preferred embodiment of the method according to the invention,
    FIG. 3
    a schematic sketch of the geometric relationships of the test object, the test head and a material error in the preferred embodiment of the method according to the invention,
    FIG. 4
    a schematic sectional view of the test object and a focusing probe according to the prior art, and
    FIG. 5
    a schematic sectional view of the test object and a test head according to the SAFT method according to the prior art.
  • FIG. 1 shows a schematic sectional view of a test object 10. The test object 10 is cylindrical. The test object 10 has a bore 12, which is aligned concentrically to the test object 10. The bore 12 and the test object 10 thus have a common rotational symmetry axis 14, which in FIG. 1 extends perpendicular to the plane of the drawing. The test object 10 has an outer radius r a and an inner radius r i . The inner radius r i of the test object 10 thus corresponds to the radius of the bore 12. In this specific embodiment, the test object 10 is a turbine disk for a gas or steam turbine.
  • On the lateral surface of the test object 10 is a test head 16. The test head 16 includes an ultrasonic transmitter and an ultrasound detector. In the test article 10, a tangential material defect 18 and a radial material defect 20 are also shown. The material defects 18 and 20 each form a cavity in the test article 10. The tangential material defect 18 extends with respect to the cylindrical test article 10 substantially in the tangential direction. Accordingly, the radial material defect 20 extends substantially in the radial direction with respect to the test article 10.
  • The material testing is done by moving the test head 16 on the outer surface of the test article 10. FIG. 1 illustrates that a radial sound wave 22 is particularly strongly reflected on the tangential material defect 18 because the tangential material defect 18 is oriented substantially parallel to the surface of the test article 10. It also becomes clear that a tangential sound wave 24 is reflected particularly intensely on the radial material defect 18.
  • Conversely, it becomes clear that the tangential sound wave 24 would only be reflected very weakly on the tangential material defect 18. Also, the radial sound wave 22 would be little reflected on the radial material defect 20.
  • In the method according to the invention, the sonication of the signal from the test head 16 takes place at different angles. In this case, either the test head 16 itself or at least its sound-emitting component is pivotable such that the entire volume of the test object 10 is accessible by scanning the outer peripheral surface. In particular, material defects 20 whose extent parallel to the surface of the test object 10 are relatively small are thereby more easily detected. This is achieved in the case of the cylindrical test object 10, for example, by virtue of the fact that the insonification direction has a tangential component in addition to the radial component. Also An insonification with a radial and an axial would be possible. Finally, the insonification can also be composed of a radial, tangential and axial component.
  • In the method according to the invention, it is not absolutely necessary that the entire surface or the entire surface portion is scanned in order to detect the entire volume of the test object 10. For example, it is possible to scan a certain distance or a specific path on the surface, since by pivoting the test head 16 at least the relevant area of the volume can be detected even without the complete scanning of the surface.
  • In FIG. 2 is a schematic sectional view from above of the test object 10 and the test head 16 according to the embodiment in FIG. 1 shown. FIG. 2 shows the bore 12, the rotational symmetry axis 14 and the radial sound wave 22. The axial material defect 26 has a sufficiently large extent at least in the axial direction. FIG. 2 illustrates that the radial sound wave 22 is reflected by the axial material error 26 sufficiently strong. The tangential sound wave 24 would also be sufficiently strongly reflected by the axial material defect 26 at a not too large insonification angle.
  • FIG. 3 shows a schematic sketch of the geometric relationships of the test article 10, the test head 16 and a material error 28 in the preferred embodiment of the method according to the invention. Between the material error 28 and the rotational symmetry axis 14, a radial distance r s is defined. The sound path s from the probe 16 to the material defect 28 is given by: s = r a 2 - r i 2 ,
    Figure imgb0001
  • The angle between the sound path s and the surface normal r a forms the insonification angle α or the insonification direction. The sound path s and the corresponding distance vector r s of the material error 28 form a right angle β.
  • By using the focusing probe 16, the sound pressure in the vicinity of the material defect 28 is increased. This improves the signal-to-noise ratio. However, this only makes sense within the near field. The length n of the near field is given by: n = d 2 / 4 λ ,
    Figure imgb0002
  • Here d is the width of the probe 16 and λ is the wavelength of the sound wave. At a typical wavelength of λ = 5 mm and a desired near-field length of n = 1 m, a test head 16 with a width of d = 140 mm is required. With the SAFT method, this near-field length n can also be achieved without this width. The SAFT method simulates a wide probe and thus achieves virtual focusing.
  • The amplitude of the reflected sound wave depends on the one hand on the spatial extent of the material defect 28 and on the other hand on the reflection properties at the interface of the material defect 28.
  • There are typically two types of noise signals in the ultrasound measurement. The first noise signal is the noise that occurs in any electronic detection system, especially in the amplifiers. This can be reduced by averaging. There is no correlation between the first noise signal and the reflected sound signal, in particular no phase correlation. The summation of the signals therefore leads to an averaging of the noise signals. With an increasing number of summands the sum of these noise signals goes to zero, if the noise signals no DC voltage component included. In practice, either no or only a small DC component occurs.
  • The second noise signal comes from the test object itself. The reflections on the microstructure of the metal form a noise carpet, which correlates with the reflected sound signal. The noise carpet is also a reflected sound signal. It arises from reflections in polycrystalline materials at their grain boundaries and in regions of different orientation of the crystal axes. Crystals are acoustically anisotropic, so that the wave resistance changes at the grain boundaries. In practice this affects all metal materials. The individual reflections on the basis of the microstructure are not disturbing, but in broad areas of the test object 10, the noise signal comes about in this way.
  • The reflections on the structure and on the material defects can be separated by the SAFT process. The Gefügerauschen shows a spatial statistics. The reflections on the microstructure are phase-correlated. The summation in the SAFT algorithm nevertheless leads to a relative weakening of the reflections on the microstructure, since the grain boundaries reflect less than the material errors. If an amplitude sum is achieved by a coincidentally in-phase superposition of the amplitudes of several grain boundaries, then their angle is narrowed even more. As the angular interval increases, the amplitudes due to material defects increase more than the amplitudes caused by the grain boundaries.
  • For example, a test head 16 with a diameter of d = 24 mm is used for the method according to the invention. In the SAFT algorithm according to the invention, the sound field of the test head 16 is taken into account. In contrast, in the known SAFT algorithm, the size of the probe 16 is neglected.
  • The detected signal is produced in particular by the reflected portion of an ultrasonic pulse at sudden spatial changes in the characteristic impedance in the test object 10. These changes are interpreted as material defects if there are no design-related material boundaries or material transitions. The detected signal contains only information about the amplitude and the transit time. Since the speed of sound in the material of the test object 10 is known, the distance can also be determined from the transit time. For spatial determination in the lateral direction, the spatial distribution of the sound field and the sensitivity of the test head 16 can be used.
  • The signals with the amplitude and the transit time, which are detected along the way by the test head 16, are added up with respect to the location in the test object 10 with the correct time. As a result of this locally correct assignment to the correct location, the amplitude sum of the signals coming from a specific location in the test object increases by its amplitude with each added signal. However, the amplitudes depend on the position of the probe 16 and thus on the relative position of the material defect 28 within the sound field.
  • The mean value of the amplitude of a material defect without directivity is proportional to its reflectance weighted by a factor k. The factor k is a value for the average sensitivity along the path of the material error 18 through the sound field of the test head 16. In this way, the detected amplitude can be meaningfully evaluated.
  • In the method according to the invention, not individual detected amplitudes are evaluated as a function of time, but the calculated spatial amplitude distributions. These can be reconstructed by the SAFT method. The calculated spatial amplitude distributions have a higher signal-to-noise ratio than the directly detected amplitudes. In this way, material defects can be identified more easily.
  • The method according to the invention makes it possible to extend the application of the reflector evaluation according to the AVG method at small amplitudes by a relative reduction of the noise, as would be possible with the use of wide probes 16. This is based on the assumption that the small amplitude is due to the small size of the reflector. Therefore, the low directivity of the reflector, which is due to the diffraction, only a negligible effect on the detected amplitude.
  • In particular, the method according to the invention makes it possible to examine large test objects 10 with correspondingly large sound paths. These large sound paths cause the low amplitudes.
  • The inventive method is applicable to known classical testing techniques in which the test object is mechanically scanned and the location or the movement of the probe 16 is known to each detected amplitude-transit time diagram.
  • The evaluation of the amplitude is carried out by first the reflector is scanned by the sound field. The angular dependence of the amplitude within the sound field is known. M amplitudes are summed in a defined angular interval Δγ about the acoustic axis. This results in a clear relationship between the sum of the amplitudes H Sum and the size of a reference reflector which would produce the same amplitude sum H Sum .
  • The amplitude sum H Sum is given by: H Sum = Σ H i γ i .
    Figure imgb0003
    wherein is summed over the number m of the detected amplitudes. H i are the detected amplitudes in the individual measurements and γ i the angular distance to the acoustic axis. At a fixed distance of the measuring points and the angular distances in the individual measurements are approximately equidistant. As the number m of the individual measurements increases, the correction factor k approaches a threshold corresponding to the average sensitivity in the angular interval Δγ. The distance between the material defect 18 and the test head 16 that is relevant for the AVG process results from the position of the test head 16 when the specific location of the material defect 18 lies on the acoustic axis.
  • Between the sum of the amplitudes H Sum and the amplitude H AVG according to the AVG method, the relation exists: H AVG = H Sum / m * k .
    Figure imgb0004
    where m is the number of individual measurements and k is a correction factor. The correction factor k is given by: k = 1 / m Σ H 0 γ i .
    Figure imgb0005
    wherein is summed over the number m of the detected amplitudes. Here, H 0i ) is the angle-dependent amplitude distribution in the sound field of the test head 16, which is normalized to H 0 (γ = 0) = 1.
  • With increasing size of the material error, ie the reflector, its directivity also increases. This may lead to an underestimation of the amplitude in the angular interval Δγ for larger material errors and at an average skew and should therefore be taken into account. In particular, the method is suitable for minor material defects whose directivity is of minor importance.
  • In FIG. 4 is a schematic sectional view of the test object 10 and a focussing probe 16 according to the prior art shown. The test article 10 has a material defect 30. On the outside of the test object 10 is the test head 16, which is designed as a focusing probe. From the probe 16 focused sound waves 32, 34 and 36 are emitted.
  • The solid line represents the wavefront of the current sound wave 32. The dashed lines represent the wavefronts of the earlier sound waves 34 and the later sound waves 36. The focused sound waves 32, 34 and 36 propagate along a predetermined direction with laterally limited extension. The focused sound waves 18 and 20 thus do not propagate globally in the entire half space.
  • The probe 16 moves along the scan 10 surface along a scan direction 38 during scanning. However, focus only occurs within the near field of the probe 16. The greater the width of the test head 16 perpendicular to the emission direction, the greater the length of the near field and thus the penetration depth of the focused sound waves 32, 34 and 36.
  • FIG. 5 shows a schematic sectional view of the test object 10 and the test head 16 according to the SAFT method according to the prior art. The test object 10 is shown with the material error 30. On the outside of the test object 10 is the test head 16. The test head 16 has compared to FIG. 4 a relatively small diameter and is not focused.
  • From the test head 16 spherical shell-shaped sound waves 42, 44 and 46 are emitted. The wavefront of the current spherical shell-shaped sound wave 42 is represented by a solid line. The dashed lines represent the wavefronts of the former spherical shell-shaped Sound waves 44 and the later spherical shell-shaped sound waves 46. A comparison of FIG. 4 and FIG. 5 illustrates that the wavefronts 32, 34 and 36 on the one hand and 42, 44 and 46 on the other hand are oppositely curved.
  • The test object 10 is subdivided by a computer into volume elements in this SAFT method. Each volume element is considered as a reflector during the scan. The reflected signal components from different positions of the probe 16, which belong to the same volume element, are recorded and added in phase with the assistance of the computer. In this way, echo signals of large amplitude are obtained only for those places with actual reflection due to constructive interference.
  • For locations without actual reflection, the echo signals are canceled due to destructive interference. The scanning and arithmetic operation simulates constructive interference an ultrasonic detector whose size corresponds to the scanned area. In this known SAFT method, the insonification angle is always 0 ° and the entire surface of the test object 10 is scanned.
  • According to the invention, in contrast, the insonification angle α can be varied.
  • The method according to the invention is not limited to the cylindrical test object 10, such as wheel disks or shafts. The insonification direction can be composed of suitable base vectors, which are adapted to the geometric shape of the test object 10.
  • Furthermore, with a suitable choice of the pivot axes of the test head 16, it may be sufficient that it is not necessary to scan an entire surface, but only along a predetermined path or a predetermined path. The inventive method thus opens up several Possibilities to adequately capture the entire volume of the test article 10.
  • The method according to the invention leads to a substantial improvement in the detectability of small material defects and those which are located deep inside the test object 10.

Claims (17)

  1. Method for nondestructive material testing of an at least sectionally solid test object (10) by the application of ultrasonic waves (20, 24) to the test object (10) and the detection of the ultrasonic waves reflected inside the test object (10), the method having the following steps:
    a) computer-aided subdivision of the test object (10) into a predetermined number of volume elements,
    b) application of ultrasound to the test object (10) at a multiplicity of surface elements while scanning the surface of at least one surface section of the test object (10),
    c) detection of the sound waves reflected at the volume elements while scanning the multiplicity of surface elements on the surface or at least on the surface section of the test object (10), and
    d) in-phase addition of the sound waves reflected at the same volume elements and detected at various surface elements of the surface of the test object (10),
    characterized in that
    e) consideration is given to an angle-dependent amplitude distribution (H0) in the sound field of a test head (16), in order to consider different sensitivities that depend on the angle,
    - the angle-dependent amplitude distribution (H0) in the sound field of the test head (16) is used to determine the amplitudes of the reflected sound waves
    - in step d) the amplitudes of the sound waves are added up in phase within a predetermined angular interval (Δγ) about the acoustic axis of the sound field of the test head (16), and
    - a specific number (m) of amplitudes are summed within the predetermined angular interval (Δγ) about the acoustic axis, in order to calculate the size of a reference reflector that would produce the same amplitude sum (Hsum).
  2. Method according to Claim 1, characterized in that the angle-dependent amplitude distribution (H0) is used to determine a correction factor (k) that corresponds to the mean sensitivity along the path through the sound field of the test head (16).
  3. Method according to either of the preceding claims, characterized in that the application of ultrasound to the test object (10) is performed at various insonification angles (α) with reference to the surface element on the surface of the test object (10).
  4. Method according to Claim 3, characterized in that the insonification angles (α) lie within a cone whose axis of symmetry forms the normal to the respective surface element.
  5. Method according to one of the preceding claims, characterized in that the surface or at least the surface section of the test object (10) is scanned along a predetermined line.
  6. Method according to one of the preceding claims, characterized in that the surface or at least the surface section of the test object (10) is scanned in accordance with a predetermined scheme.
  7. Method according to one of the preceding claims, characterized in that the surface or at least the surface section of the test object (10) is completely scanned.
  8. Method according to one of the preceding claims and one of Claims 3 and 4, characterized in that the insonification angles (α) are between 0° and 50°, preferably between 0° and 30°.
  9. Method according to one of the preceding claims, characterized in that the method is provided for an at least sectionally rotationally symmetrical test object (10).
  10. Method according to one of the preceding claims, characterized in that the method is provided for an at least sectionally cylindrical test object (10).
  11. Method according to Claim 10, characterized in that the insonification direction has a radial, tangential and/or axial component with reference to the surface of the cylindrical test object (10).
  12. Method according to one of the preceding claims, characterized in that the method is provided for the material testing of a test object (10) made from metal.
  13. Method according to one of the preceding claims, characterized in that the method is provided for the material testing of a forged component (10).
  14. Method according to one of the preceding claims, characterized in that the method is provided for the material testing of a turbine wheel.
  15. Device for nondestructive material testing of an at least sectionally solid test object (10), which device has at least one test head (16) for the emission of ultrasonic waves (20, 24) and for the detection of the ultrasonic waves reflected inside the test object (10),
    characterized in that
    a computer is present which is set up to carry out the steps of the method according to at least one of Claims 1 to 14.
  16. Device according to Claim 15, characterized in that the test head (16) or at least its component emitting sound is swivel mounted such that the insonification direction can be varied with reference to the surface normal to the surface of the test object (10).
  17. Device according to Claim 15 or Claim 16, characterized in that the test head (16) is mounted to swivel between 0° and 60°, preferably between 0° and 30°, with reference to the surface normal to the surface of the test object (10).
EP20080735834 2007-05-15 2008-04-04 Method and device for non-destructive material testing of a test object using ultrasonic waves Active EP2147300B8 (en)

Priority Applications (2)

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PCT/EP2008/054093 WO2008138684A1 (en) 2007-05-15 2008-04-04 Method and device for non-destructive material testing of a test object using ultrasonic waves

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EP12001837.9 Division-Into 2012-03-19

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CN101711358A (en) 2010-05-19
WO2008138684A1 (en) 2008-11-20
KR101197323B1 (en) 2012-11-05
EP2147300B8 (en) 2013-01-23
EP2147300A1 (en) 2010-01-27
KR20100021463A (en) 2010-02-24
CN101711358B (en) 2013-07-24
RU2423690C1 (en) 2011-07-10
EP2469276A1 (en) 2012-06-27
US8656782B2 (en) 2014-02-25
EP2469276B1 (en) 2017-03-08
JP5094963B2 (en) 2012-12-12
JP2010527015A (en) 2010-08-05

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